Finally. After nearly a year of posting about science from the Big Ten, I have a reason to write a post about my favorite topic of all. That’s right, kids, today we’re going to talk about beer. But not just any beer. No, we’re going to talk about lagers. Perhaps you need a little bit of background and an education about the delicious suds you’ve been drinking all these years.

There are two types of beer – ales and lagers – and the difference comes in the type of yeast that turns the sugar of the wort (sugars extracted from grain dissolved into water with hops and what not) into alcohol. In ales, the different strains of yeast float towards the top of the liquid and work best in warmer environments, say 68 to 72 degrees. Lagers, on the other hand, sink to the bottom and thrive in temperatures a tad cooler, somewhere between 45 and 55 degrees (more ore less).

The difference in taste and appearance is quite clear. Ales create cloudy, thicker, richer beers. Some good style examples are pale ales, IPAs, stouts, porters, amber ales and more. Lagers are clearer and crisper. Examples include all light American beers, their full-flavored counterparts, and all the German beers that those are derived from – pilsners, bocks, marzens and kolschs.

It may seem odd that all the beers you are familiar with that are lagers are also German. But it’s not strange at all. The Germans invented lager brewing back in the 15th century.

And thank God they did.

Now, I’m going to take a quick turn and talk about domestication. I’m sure animals such as dogs, cats, cows and other farm animals immediately jump to mind. Humans have long tamed wild animals and slowly bred them to serve their purposes. But what might not jump immediately to mind are microbes.

Just like the larger four-legged creatures, bacteria have also been domesticated over the years. Since humans have been baking bread, making wine and brewing beer for thousands of years, we’ve inadvertently selected for the yeast strains and mutations that work the best for each of these culinary necessities. So much so that some strains of yeast can’t be found in nature. They’ve cross bred and fused with other species in the fermentation barrels of alcohol makers around the world in order to thrive in these conditions. And since most brewers simply take the yeast from one batch and use it again in the next, they’ve come to be distinct species.

For example, the primary yeast used for lagering is known as Saccharomyces pastorianus, and it does not exist in the wild. Half of its genome comes from an ale yeast called Saccharomyces cerevisiae. The other half comes from a species that thrives in the chilly conditions that the hybrid prefers. However, nobody knows where that second half of the genome came from.

Scientists at the University of Wisconsin (leave it to Wisconsin to conduct beer research) recently were conducting a survey of wild yeast strains with colleagues around the world in order to try to locate the missing half of the genome. And they found it. In the forests of Patagonia.

That’s right, the yeast strain responsible for lagers came all the way from the southern tip of South America.

The known half of S. pastorianus comes from a yeast strain that grows wild on oak trees in the temperate regions of Europe. Chances were likely that the other half had to come from a similar strain, but one that was used to colder climates. So coauthor Chris Todd Hittinger and colleagues took their search to the beech forests of the alpine region of South America. Beech trees fill the same ecological niche as oaks and indeed are closely related. And in the cold climate of Patagonia, it seemed logical that similar but cold-temperature-resistant strains of bacteria would be thriving there.

Orange-colored galls, such as these pictured in 2010, from the beech tree forests of Patagonia have been found to harbor the yeast that makes lager beer possible. Five hundred years ago, in the age of sail and when the trans-Atlantic trade was just beginning, the yeast somehow made its way from Patagonia to the caves and monastery cellars of Bavaria where the first lager beers were fermented. University of Wisconsin-Madison Genetics Professor Chris Todd Hittinger and colleagues from Portugal, Argentina and the University of Colorado describe the lager yeast, whose origin was previously unknown. (Photo by Diego Libkind, Institute for Biodiversity and Environment Research, Bariloche, Argentina)

The new strain of yeast – dubbed S. eubayanus – makes its home in the Beech galls of South America. Very rich in simple sugars, the large, round, orange outgrowths in the tree fall to the forest floor and naturally ferment. It’s this fermentation that initially piqued the interest of scientists who wondered what yeast was responsible.

But still, 7,000 miles is a long ways to look for a simple yeast strain. Especially since it seems to have originated at the very beginning of trans-Atlantic voyages. But apparently, at some point in the very beginnings of those voyages, the bacteria somehow made its way to the caves and monasteries of Bavaria.

Scientists postulate that the yeast may have stowed away on a piece of wood or in the stomach of a fruit fly overseas. Whatever they way, it ended up in the fermentation barrels of German monks, where it fused with S. cerevisiae to form a type of “proto-lager” yeast strain. Hundreds of years and millions of batches of lager later, the yeast strain has underwent slight mutations and changes to become the lager-brewing strain we know and love today.